1. Field of the Invention
The invention relates to producing a hydrocarbon feedstock having lower concentrations of carbon formers and metals, which feedstock can be used for heavy hydrocarbon conversion processes, such as the RCC.SM. process, and/or for the conventional fluid catalytic cracking (FCC) processes. More particularly, the invention is directed to the use of a relatively inert sorbent material composition as a means for removing the carbon formers and metals from the particular hydrocarbon stream in the presence of steam and the subsequent regeneration of the aforesaid sorbent material composition by treating the spent sorbent composition in an environment containing both steam and oxygen-containing gas under selected conditions.
2. Description of the Prior Art
In the 1960's, molecular sieves or zeolites were incorporated into the FCC catalysts. These zeolitic-containing catalysts revolutionized the FCC process. Such catalysts were considerably more active for cracking hydrocarbons than were the earlier amorphous or amorphous/kaolin-containing silica-alumina catalysts. These active catalysts caused various innovations to be developed to handle their high activities. Such innovations included riser cracking, shortened contact times, new regeneration processes, and improved catalysts containing molecular sieves or zeolites.
Subsequently, the petroleum industry began to suffer from a lack of crude availability as to quantity and quality accompanied by increasing demand for gasolines having increased octane values. The supply situation changed from a surplus of light, sweet crudes to a tighter supply having an increasing amount of heavier crudes containing higher amounts of sulfur and nitrogen. Often such heavier crudes also contained much higher concentrations of metals and carbon formers, along with increased amounts of asphaltic components.
Such metal contaminants and carbon formers have a rather severe deleterious effect upon such FCC molecular sieve-containing catalysts. They lower the activity and selectivity of the catalyst for producing liquid fuel products. Furthermore, they result in a reduced catalyst life.
Heavier crude oils contain more asphaltenes and polycyclic compounds that yield less or a lower volume of a high quality FCC gas oil charge stock. Such gas oil charge stock normally boils below a temperature of about 552.degree. C. (1,025.degree. F.), and is generally processed to contain a total metals level that is less than 1 ppm, preferably below 0.1 ppm, and Conradson carbon values that are substantially below 1 wt. %.
The need to process heavier and less desirable crudes caused the petroleum industry to search for and provide processing schemes which could utilize such heavier crudes in producing gasoline and other liquid fuel products. The literature has described many of these processing schemes, such as Gulf Oil Corporation's Gulfining and Union Oil's Unifining processes for treating residua, UOP's Aurabon process, Hydrocarbon Research's H-Oil process, Exxon's Flexicoking process to produce thermal gasoline and coke, H-Oil's Dynacracking and Phillip's Heavy Oil Cracking processes. Such processes employ thermal cracking or hydrotreating followed by FCC or hydrocracking operations to handle the higher content of metal contaminants (Ni-V-Fe-Cu-Na) and the high Conradson carbon values of 5 wt. % to 15 wt. %. Of course, such types of processing are accompanied by various drawbacks. Coking yields thermally-cracked gasoline which has a much lower octane value than gasoline that is obtained from a catalytic cracker, is unstable due to the production of gum from diolefins, and requires further hydrotreating and reforming to produce a higher octane product. Gas oil quality is degraded due to thermal reactions which produce a product containing refractory polynuclear aromatics and high Conradson carbon levels which are quite unsuitable for catalytic cracking. Hydrotreating requires expensive high-pressure hydrogen, multi-reactor systems made of special alloys, costly operations, and quite often a separate costly facility for the production of hydrogen.
Conventional FCC practice in the past has involved the treatment of those fractions of crude oils that are relatively free of coke precursors or heavy metals, or both, and boil within the range of about 343.degree. C. (650.degree. F.) to about 538.degree. C. (1,000.degree. F.). These fractions are referred to as "vacuum gas oil" (VGO) and are conveniently prepared from a crude oil by distillation at atmospheric pressure to remove the fractions boiling below about 343.degree. C. (650.degree. F.) and then separating by vacuum distillation a cut boiling between about 343.degree. C. (650.degree. F.) and about 552.degree. C. (1,025.degree. F.) from the heavier material.
This heavier material has been used for the production of asphalt, residual fuel oil, No. 6 fuel oil, and marine Bunker C fuel oil. Of course, there is considerable economical potential if the contaminants can be removed from such heavier material in order that it can be cracked along with the lighter oils.
There has been developed a method for cracking high boiling fractions, named with the RCC.SM. Process and disclosed by Myers, e.g., in U.S. Pat. Nos. 4,332,673; 4,299,687 and 4,341,624, each incorporated herein by reference. Hydrocarbons fractions suitable for cracking by the RCC Process are carbo-metallic oils at least about 70 percent of which boils above a temperature of 343.degree. C. (650.degree. F.) and which contain a carbon residue on pyrolysis of at least about 1 wt. % and at least about 4 ppm of nickel equivalents of heavy metals. The nickel equivalents of an oil can be calculated conveniently by using the following formula which is patterned after that of W. L. Nelson in Oil and Gas Journal, page 143, October 23, 1961: EQU Nickel Equivalents=Ni+V/4.8+Fe/7.1+Cu/1.23,
wherein the content of each metal that is present is expressed as the metal in parts per million by weight of that metal, based on the weight of feed. As used herein, the term "heavy metals" refers to nickel, vanadium, copper, and iron. Trace amounts of other heavy metal elements can be present. Crude oils, topped crudes, reduced crudes, residua, and extracts from solvent deasphalting are suitable feedstocks for the RCC Process, which can handle satisfactorily reduced crudes containing a heavy metals content within the range of about 10 ppm to about 100 ppm and a Conradson carbon content within the range of about 2 wt. % to about 8 wt. %.
While the RCC Process can treat effectively many crudes, certain crudes contain abnormally high contents of heavy metals and carbon precursors. Such poor-grade crudes are Mexican Mayan crudes or Venezuelan crudes. For example, a Mayan reduced crude can contain up to 500 ppm heavy metals, or more, and have a Conradson carbon value of 8 wt. %, or higher. Of course, the processing of these poor-grade crudes can lead to an uneconomical operation, as a result of the high coke-burning load on the regenerator and the high catalyst-addition rate that would be needed to maintain the activity and selectivity of the catalyst being employed in the process. In view of this, it is desirable to develop some means that would be more economical for processing poor-grade crude oils and residual stocks.
Both the contaminant metals (Ni-V-Fe-Cu-Na) and Conradson carbon affect a cracking catalyst that contains a zeolite and the operating parameters of a catalytic cracking operation. The metal content and Conradson carbon are two very effective restraints on the operation of a FCC unit and may even impose undesirable restraints on a Reduced Crude Conversion (RCC) unit from the standpoint of obtaining satisfactory conversion, selectivity, and catalyst life. Relative low levels of such contaminants are very detrimental to FCC units that employ catalysts containing zeolites. Moreover, as metals and Conradson carbon levels are increased, the operating capacity and the efficiency of a reduced crude cracking process are adversely affected or even made uneconomical.
As the zeolite-containing cracking catalyst is employed in either a FCC process or a RCC process, carbon or coke is deposited upon the catalyst particles and such carbonaceous deposits must be substantially removed from the catalyst particles periodically to maintain the activity or reactivate the particular catalytic material. The catalyst containing the hydrocarbonaceous deposits resulting in hydrocarbon conversion is restored to an equilibrium activity by burning off the deactivating hydrocarbonaceous material and residual coke in a regeneration zone in the presence of oxygen. Such burning off of the hydrocarbonaceous material heats the catalyst to an elevated temperature. The regenerated catalyst at that elevated temperature is recycled back to the reaction zone in the particular unit that employs the catalyst. The heat that is generated during the burning of the hydrocarbonaceous material in the regeneration zone is removed, at least partially, by the heated catalyst and is carried to the reaction zone, where it can be used to help vaporize the hydrocarbon feed and to furnish heat for the endothermic cracking reaction. In addition, hot regeneration flue gases remove a portion of the regeneration heat. Generally, the temperature is maintained in the regenerator below 871.degree. C. (1,600.degree. F.), since higher temperature would be deleterious to the metallurgy of the processing vessel and to the hydrothermal stability of the catalytic material being employed.
The temperature and steam partial pressure at which the zeolite begins to rapidly lose its crystalline structure determine the hydrothermal stability of such zeolite-containing catalyst. A lower-activity material results. The presence of steam is highly critical. The steam is generated by the burning of adsorbed and adsorbed (sorbed) carbonaceous material which has a significant hydrogen content. The hydrogen-to-carbon atomic ratios are generally greater than about 0.5. The high-boiling sorbed hydrocarbons provide the hydrocarbonaceous-material deposit. The deposit is obtained particularly from asphaltic or polycyclic high molecular weight materials which do not vaporize at temperatures below 552.degree. C. (1,025.degree. F.). Such materials have a modest hydrogen content and include high-boiling nitrogen-containing hydrocarbons, as well as related high molecular weight porphyrins and asphaltenes. The high molecular weight nitrogen compounds usually do not boil or vaporize below about 552.degree. C. (1,025.degree. F.) and can be either basic or acidic in nature. The basic nitrogen compounds tend to neutralize the acid cracking sites, while those nitrogen compounds that are more acidic can be attracted to metal sites on the catalyst. The porphyrins and asphaltenes, which do not vaporize at temperatures as high as 552.degree. C. (1,025.degree. F.), may contain elements other than carbon and hydrogen. As used in this specification, the term "heavy hydrocarbons" includes all carbon- and hydrogen-containing resid compounds that do not boil or vaporize at a temperature in the range of 343.degree. C. (650.degree. F.) up to about 552.degree. C. (1,025.degree. F.), regardless of whether other elements are also present in the compound.
The heavy metals in the feedstock are generally present as porphyrins and/or asphaltenes. However, certain of these metals, particularly iron and copper, may be present as a free metal or as inorganic compounds resulting from either corrosion of process equipment or contaminants from other refining processes.
Coke production increases as the Conradson carbon value of the feedstock increases. This increased load will raise the regeneration temperature. Consequently, any given cracking-regeneration unit may be limited as to amount of feed that can be processed, because of the Conradson carbon content of the feed.
The metal-containing fractions of reduced crudes contain Ni-V-Fe-Cu in the form of porphyrins and asphaltenes. The metal-containing hydrocarbons are deposited on the catalyst during processing and are cracked in the reaction zone of the processing unit to deposit the metal with hydrocarbonaceous material on the catalyst. Such deposits are carried by the catalyst substantially as metallo-porphyrin or asphaltene to a regeneration operation and converted to the metal oxide during regeneration. As taught in the literature, the deposited metals result in non-selective or degradative cracking and dehydrogenation to produce increased amounts of deposited carbonaceous material and light gaseous products, such as hydrogen, methane, and ethane. The cracking selectivity is thus adversely affected, resulting in poor product yields and poor quality gasoline and light cycle oil. Of course, increased production of light gases puts an increased demand on the downstream gas plant gas compressor capacity. The increased coke production has a negative impact on yield, adversely affects catalyst activity-selectivity, greatly increases regenerator air demand and compressor capacity, and contributes to high regenerator temperature.
Certain crudes, such as Mexican Mayan or Venezuelan crudes, contain abnormally high metal and Conradson carbon contents and will, as a result, lead to an uneconomical operation. The high coke burning load on the regenerator and the high catalyst addition rate needed to maintain catalyst activity and selectivity prompt the uneconomical operation. In view of this, it is desirable to develop an economical means of processing poor grade crude oils, such as the Mexican Mayan or Venezuelan crudes, since such crudes are more readily available and cheaper than crudes obtained from the Middle East.
The art suggests various processes for the reduction of metals and Conradson carbon values of residual oil, topped or reduced crudes, and other contaminated high boiling oil fractions. The disclosure of each of the prior art patents and patent applications discussed hereinbelow is incorporated herein and made a part hereof by reference thereto.
For example, in U.S. Pat. No. 4,243,514, Bartholic disclosed a process which involves contacting a reduced crude fraction or other contaminated oil fraction with a sorbent material at elevated temperatures in a sorbing zone, such as in a fluid bed contact zone, to produce a product of reduced metal and Conradson carbon value. One of the sorbents is an inert solid initially composed of kaolin, which has been spray dried to yield microspherical particles having a surface area below 100 m..sup.2 /gm. and a catalytic cracking micro-activity (MAT) value of less than 20 and which is calcined at high temperature, so as to achieve better attrition resistance.
U.S. Pat. No. 4,412,924, to Hettinger, Jr., et al, discloses a process for the decarbonization-demetallization of a poor quality residual oil feed boiling above about 343.degree. C. (650.degree. F.) and comprising a substantial amount of Conradson carbon components to provide a higher grade of oil feed by contacting the poor quality oil feed with sorbant particle material containing one or more metal additives selected to catalyze the endothermic removal of coke with CO.sub.2. Selected sorbent decarbonization conditions resulted in the depositing of substantial quantities of carbonaceous material and metals on the sorbent in the decarbonizing zone. The sorbent material containing the metals and hydrocarbonaceous deposits is then regenerated in the presence of gas streams containing oxygen and carbon dioxide in separate sorbent regeneration zones at a temperature that is sufficiently elevated to remove the residual coke to a desired low level. The regenerated sorbent particle material at an elevated temperature below about 816.degree. C. (1,500.degree. F.) is recycled to the decarbonizing zone for contact with additional feed.
U.S. Pat. No. 4,417,975 to Myers et al discloses a carbo-metallic oil conversation process wherein the temperature within a catalyst regenerator is controlled by introducing liguid water into a catalyst bed in the regenerator.
U.S. Pat. No. 4,432,863 to Myers et al discloses a process of economically converting carbo-metallic oils to liquid fuel products wherein a suspension of particulate cracking catalysts and carbo-metallic oil is passed through a riser reaction zone, the coke-laden catalyst is separated from the resulting stream of hydrocarbons, the coke-laden catalyst is stripped and regenerated, and the regenerated catalyst is contacted with a reducing gas under reducing conditions sufficient to reduce at least a portion of the oxidized metal deposits to a reduced state. Then the reduced catalyst is sent to the conversion zone for contact with fresh carbo-metallic oil. Water is introduced into the riser reactor conversion zone in an amount, which when coupled with a selected amount of reduced nickel on the recycled catalyst, is sufficient to provide steam reforming, which results in hydrogen-deficient components of the feed being converted to products having higher ratios of hydrogen to carbon and a reduced amount of feed being converted to coke.
U.S. Pat. No. 4,417,975, to Myers et al discloses that water can be added to the oxygen-containing gas introduced into the regenerator to control the heat load in the regenerator of a fluid catalyst system.
The present invention is directed to the use of an inert sorbent to remove carbon formers or carbon precursors (heptane-insoluble material) and metals that are present in a carbo-metallic oil at elevated temperatures and in the presence of steam in a riser reaction zone, promoting the reaction of carbon and the formation of hydrogen, the separation of the resulting gaseous products from the spent coked sorbent, the stripping and regeneration of the spent coked sorbent in the presence of an oxygen-steam environment at elevated temperatures to remove the carbonaceous deposits by means of oxidation, water gas reaction, carbon gasification, and possibly some steam reforming and the recycling of the regenerated sorbent to the riser reaction zone.
The invention provides a means for handling those reduced crudes that are not amenable to reduced crude treating operations as a result of high-metals content and high Conradson carbon content. The process of this invention will remove a major portion of the metals and heptane-insoluble material and, depending upon the severity, will yield a product that is amenable to processing in a RCC or FCC unit.